1. Guide to Computer Forensics and Investigations Fifth Edition
Chapter 5
Working with Windows and CLI Systems
CLI – command-line interface
All slides copyright Cengage Learning with additional info from G.M. Santoro

2. Understanding File Systems
Gives OS a road map to data on a disk
Type of file system an OS uses determines how data is stored on the disk
When you need to access a suspect’s computer to acquire or inspect data
You should be familiar with both the computer’s OS and file systems
In some cases your forensics software will detect this for you.
If you anticipate a manual analysis, knowing the OS and file system is important.
Guide to Computer Forensics and Investigations, Fifth Edition

3. Understanding the Boot Sequence
Complementary Metal Oxide Semiconductor (CMOS)
Computer stores system configuration and date and time information in the CMOS
When power to the system is off
Basic Input/Output System (BIOS) or Extensible Firmware Interface (EFI)
Contains programs that perform input and output at the hardware level
Guide to Computer Forensics and Investigations, Fifth Edition

4. Understanding the Boot Sequence
Bootstrap process
Contained in ROM, tells the computer how to proceed
Displays the key or keys you press to open the CMOS setup screen
CMOS should be modified to boot from a forensic floppy disk or CD
Depending on your brand of computer, various keys may be pressed during power-on to access the CMOS screen
Guide to Computer Forensics and Investigations, Fifth Edition

5. Understanding Disk Drives
Disk drives are made up of one or more platters coated with magnetic material
Disk drive components
Geometry
Head
Tracks
Cylinders
Sectors
Guide to Computer Forensics and Investigations, Fifth Edition

6. Understanding Disk Drives
Properties handled at the drive’s hardware or firmware level
Zone bit recording (ZBR)
Track density
Areal density
Head and cylinder skew
Guide to Computer Forensics and Investigations, Fifth Edition

7. Solid-State Storage Devices
All flash memory devices have a feature called wear-leveling
An internal firmware feature used in solid-state drives that ensures even wear of read/writes for all memory cells
When dealing with solid-state devices, making a full forensic copy as soon as possible is crucial
In case you need to recover data from unallocated disk space
SSD provides a challenge for forensics.
Guide to Computer Forensics and Investigations, Fifth Edition

8. Exploring Microsoft File Structures
In Microsoft file structures, sectors are grouped to form clusters
Storage allocation units of one or more sectors
Clusters range from 512 bytes up to 32,000 bytes each
Combining sectors minimizes the overhead of writing or reading files to a disk
This speeds up file I/O
Guide to Computer Forensics and Investigations, Fifth Edition

9. Exploring Microsoft File Structures
Clusters are numbered sequentially starting at 0 in NTFS and 2 in FAT
First sector of all disks contains a system area, the boot record, and a file structure database
OS assigns these cluster numbers, called logical addresses
Sector numbers are called physical addresses
Clusters and their addresses are specific to a logical disk drive, which is a disk partition
Guide to Computer Forensics and Investigations, Fifth Edition

10. Disk Partitions A partition is a logical drive
Windows OSs can have three primary partitions followed by an extended partition that can contain one or more logical drives
Hidden partitions or voids
Large unused gaps between partitions on a disk
Partition gap
Unused space between partitions
Data can be hidden in the partition gap – a complete drive image will preserve this data
Guide to Computer Forensics and Investigations, Fifth Edition

11. Disk Partitions The partition table is in the Master Boot Record (MBR)
Located at sector 0 of the disk drive
MBR stores information about partitions on a disk and their locations, size, and other important items
In a hexadecimal editor, such as WinHex, you can find the first partition at offset 0x1BE
The file system’s hexadecimal code is offset 3 bytes from 0x1BE for the first partition
This is one way to know that a hidden partition exists on a drive.
Guide to Computer Forensics and Investigations, Fifth Edition

12. Examining FAT Disks File Allocation Table (FAT)
File structure database that Microsoft originally designed for floppy disks
FAT database is typically written to a disk’s outermost track and contains:
Filenames, directory names, date and time stamps, the starting cluster number, and file attributes
Three current FAT versions
FAT16, FAT32, and exFAT (used by Xbox game systems)
Guide to Computer Forensics and Investigations, Fifth Edition

13. Examining FAT Disks
Microsoft OSs allocate disk space for files by clusters
Results in drive slack
Unused space in a cluster between the end of an active file and the end of the cluster
Drive slack includes:
RAM slack and file slack
An unintentional side effect of FAT16 having large clusters was that it reduced fragmentation
As cluster size increased
Slack can be used to hide data
It is very simple to use a hex editor to place text messages in file slack space (such as a music file)
Guide to Computer Forensics and Investigations, Fifth Edition

14. Examining FAT Disks When you run out of room for an allocated cluster
OS allocates another cluster for your file, which creates more slack space on the disk
As files grow and require more disk space, assigned clusters are chained together
The chain can be broken or fragmented
When the OS stores data in a FAT file system, it assigns a starting cluster position to a file
Data for the file is written to the first sector of the first assigned cluster
Guide to Computer Forensics and Investigations, Fifth Edition

15. Examining FAT Disks
When this first assigned cluster is filled and runs out of room
FAT assigns the next available cluster to the file
If the next available cluster isn’t contiguous to the current cluster
File becomes fragmented
Older systems could get a speed boost by de-fragmentation of its drives.
This is less of an issue today.
Guide to Computer Forensics and Investigations, Fifth Edition

16. Deleting FAT Files In Microsoft OSs, when a file is deleted
Directory entry is marked as a deleted file
With the HEX E5 character replacing the first letter of the filename
FAT chain for that file is set to 0
Data in the file remains on the disk drive
Area of the disk where the deleted file resides becomes unallocated disk space
Available to receive new data from newly created files or other files needing more space
So it is possible to recover the file as long as the original data has not been overwritten
Guide to Computer Forensics and Investigations, Fifth Edition

17. Examining NTFS Disks NT File System (NTFS)
Introduced with Windows NT
Primary file system for Windows 8
Improvements over FAT file systems
NTFS provides more information about a file
NTFS gives more control over files and folders
NTFS was Microsoft’s move toward a journaling file system
It records a transaction before the system carries it out
New Technology File System
Guide to Computer Forensics and Investigations, Fifth Edition

18. Examining NTFS Disks
In NTFS, everything written to the disk is considered a file
On an NTFS disk
First data set is the Partition Boot Sector
Next is Master File Table (MFT)
NTFS results in much less file slack space
Clusters are smaller for smaller disk drives
NTFS also uses Unicode
An international data format
NTFS follows the Unix strategy – everything on a disk is a file – however there are various properties for files that distinguish their use
Guide to Computer Forensics and Investigations, Fifth Edition

19. NTFS System Files MFT contains information about all files on the disk
Including the system files the OS uses
In the MFT, the first 15 records are reserved for system files
Records in the MFT are called metadata
Metadata means ‘data about data’
Guide to Computer Forensics and Investigations, Fifth Edition

20. MFT and File Attributes
In the NTFS MFT
All files and folders are stored in separate records of 1024 bytes each
Each record contains file or folder information
This information is divided into record fields containing metadata
A record field is referred to as an attribute ID
File or folder information is typically stored in one of two ways in an MFT record:
Resident and nonresident
Guide to Computer Forensics and Investigations, Fifth Edition

21. MFT and File Attributes
Files larger than 512 bytes are stored outside the MFT
MFT record provides cluster addresses where the file is stored on the drive’s partition
Referred to as data runs
Each MFT record starts with a header identifying it as a resident or nonresident attribute
Very small files (under 512 bytes) are resident.
Guide to Computer Forensics and Investigations, Fifth Edition

22. MFT and File Attributes
When a disk is created as an NTFS file structure
OS assigns logical clusters to the entire disk partition
These assigned clusters are called logical cluster numbers (LCNs)
Become the addresses that allow the MFT to link to nonresident files on the disk’s partition
When data is first written to nonresident files, an LCN address is assigned to the file
This LCN becomes the file’s virtual cluster number (VCN)
Guide to Computer Forensics and Investigations, Fifth Edition

23. NTFS Alternate Data Streams
Ways data can be appended to existing files
Can obscure valuable evidentiary data, intentionally or by coincidence
In NTFS, an alternate data stream becomes an additional file attribute
Allows the file to be associated with different applications
You can only tell whether a file has a data stream attached by examining that file’s MFT entry
Some forensics software will detect and display alternate data streams
For more on ADS see
Guide to Computer Forensics and Investigations, Fifth Edition

24. NTFS Compressed Files
NTFS provides compression similar to FAT DriveSpace 3 (a Windows 98 compression utility)
Under NTFS, files, folders, or entire volumes can be compressed
Most computer forensics tools can uncompress and analyze compressed Windows data
This compression has the goal of saving drive space
Guide to Computer Forensics and Investigations, Fifth Edition

25. Deleting NTFS Files When a file is deleted in Windows NT and later
The OS renames it and moves it to the Recycle Bin
Can use the Del (delete) MS-DOS command
Eliminates the file from the MFT listing in the same way FAT does
Guide to Computer Forensics and Investigations, Fifth Edition

26. Resilient File System
Resilient File System (ReFS) - designed to address very large data storage needs
Such as the cloud
Features incorporated into ReFS’s design:
Maximized data availability
Improved data integrity
Designed for scalability
ReFS uses disk structures similar to the MFT in NTFS
Guide to Computer Forensics and Investigations, Fifth Edition

27. Understanding Whole Disk Encryption
In recent years, there has been more concern about loss of
Personal identity information (PII) and trade secrets caused by computer theft
Of particular concern is the theft of laptop computers and other handheld devices
To help prevent loss of information, software vendors now provide whole disk encryption
Removable drives should also have whole disk encryption
Guide to Computer Forensics and Investigations, Fifth Edition

28. Understanding Whole Disk Encryption
Current whole disk encryption tools offer the following features:
Preboot authentication
Full or partial disk encryption with secure hibernation
Advanced encryption algorithms
Key management function
Guide to Computer Forensics and Investigations, Fifth Edition

29. Understanding Whole Disk Encryption
Whole disk encryption tools encrypt each sector of a drive separately
Many of these tools encrypt the drive’s boot sector
To prevent any efforts to bypass the secured drive’s partition
To examine an encrypted drive, decrypt it first
Run a vendor-specific program to decrypt the drive
Many vendors use a bootable CD or USB drive that prompts for a one-time passphrase
Encryption is tricky – it may be possible to decrypt an encrypted drive but it may not be.
Under current law a suspect can be forced to provide an decryption passphrase if other evidence shows that the drive holds evidence.
Otherwise this could be in violation of the 5’th Amendment.
Guide to Computer Forensics and Investigations, Fifth Edition

30. Understanding the Windows Registry
A database that stores hardware and software configuration information, network connections, user preferences, and setup information
To view the Registry, you can use:
Regedit (Registry Editor) program for Windows 9x systems
Regedt32 for Windows 2000, XP, and Vista
Both utilities can be used for Windows 7 and 8
The Registry stores a lot of data of possible use.
Be careful when playing with a registry editor!
Guide to Computer Forensics and Investigations, Fifth Edition

31. Exploring the Organization of the Windows Registry
Registry terminology:
Registry
Registry Editor
HKEY
Key
Subkey
Branch
Value
Default value
Hives
Registry files are located in different parts of the primary drive – according to function
Guide to Computer Forensics and Investigations, Fifth Edition

32. Understanding Microsoft Startup Tasks
Learn what files are accessed when Windows starts
This information helps you determine when a suspect’s computer was last accessed
Important with computers that might have been used after an incident was reported
This is one reason why a static acquisition is preferable – to prevent the startup process from writing to the drive.
Guide to Computer Forensics and Investigations, Fifth Edition

33. Startup in Windows 7 and Windows 8
Windows 8 is a multiplatform OS
Can run on desktops, laptops, tablets, and smartphones
The boot process uses a boot configuration data (BCD) store
The BCD contains the boot loader that initiates the system’s bootstrap process
Press F8 or F12 when the system starts to access the Advanced Boot Options
Guide to Computer Forensics and Investigations, Fifth Edition

34. Startup in Windows NT and Later
All NTFS computers perform the following steps when the computer is turned on:
Power-on self test (POST)
Initial startup
Boot loader
Hardware detection and configuration
Kernel loading
User logon
Guide to Computer Forensics and Investigations, Fifth Edition

35. Startup in Windows NT and Later
Startup Files for Windows Vista:
The Ntldr program in Windows XP used to load the OS has been replaced with these three boot utilities:
Bootmgr.exe
Winload.exe
Winresume.exe
Windows Vista includes the BCD editor for modifying boot options and updating the BCD registry file
The BCD store replaces the Windows XP boot.ini file
Guide to Computer Forensics and Investigations, Fifth Edition

36. Startup in Windows NT and Later
Startup Files for Windows XP:
NT Loader (NTLDR)
Boot.ini
Ntoskrnl.exe
Bootvid.dll
Hal.dll
BootSect.dos
NTDetect.com
NTBootdd.sys
Pagefile.sys
Guide to Computer Forensics and Investigations, Fifth Edition

37. Startup in Windows NT and Later
Contamination Concerns with Windows XP
When you start a Windows XP NTFS workstation, several files are accessed immediately
The last access date and time stamp for the files change to the current date and time
Destroys any potential evidence
That shows when a Windows XP workstation was last used
Again – static acquisition is preferred if possible.
Guide to Computer Forensics and Investigations, Fifth Edition

38. Understanding Virtual Machines
Allows you to create a representation of another computer on an existing physical computer
A virtual machine is just a few files on your hard drive
Must allocate space to it
A virtual machine recognizes components of the physical machine it’s loaded on
Virtual OS is limited by the physical machine’s OS
A virtual machine simulates another computer (or operating system)
Guide to Computer Forensics and Investigations, Fifth Edition

39. Understanding Virtual Machines
In digital forensics
Virtual machines make it possible to restore a suspect drive on your virtual machine
And run nonstandard software the suspect might have loaded
From a network forensics standpoint, you need to be aware of some potential issues, such as:
A virtual machine used to attack another system or network
VMs are important to computer forensics in two ways:
1 – your forensics analysis computer may run a VM to simulate the original source computer
2 – a VM may have been used to commit a crime – knowing how to find VM tracks is useful
Guide to Computer Forensics and Investigations, Fifth Edition

40. This concludes Topic 5.
Guide to Computer Forensics and Investigations, Fifth Edition